Traditionally, predictive growth models for food pathogens are developed based on experiments in broth media, resulting in models which do not incorporate the influence of food microstructure. The use of model systems with various microstructures is a promising concept to get more insight into the influence of food microstructure on microbial dynamics. By means of minimal variation of compositional and physicochemical factors, these model systems can be used to study the isolated effect of certain microstructural aspects on microbial growth, survival and inactivation. In this study, the isolated effect on microbial growth dynamics of Listeria monocytogenes of two food microstructural aspects and one aspect influenced by food microstructure were investigated, i.e., the nature of the food matrix, the presence of fat droplets, and microorganism growth morphology, respectively. To this extent, fish-based model systems with various microstructures were used, i.e., a liquid, a second more viscous liquid system containing xanthan gum, an emulsion, an aqueous gel, and a gelled emulsion. Growth experiments were conducted at 4 and 10 °C, both using homogeneous and surface inoculation (only for the gelled systems). Results regarding the influence of the growth morphology indicated that the lag phase of planktonic cells in the liquid system was similar to the lag phase of submerged colonies in the xanthan system. The lag phase of submerged colonies in each gelled system was considerably longer than the lag phase of surface colonies on these respective systems. The maximum specific growth rate of planktonic cells in the liquid system was significantly lower than for submerged colonies in the xanthan system at 10 °C, while no significant differences were observed at 4 °C. The maximum cell density was higher for submerged colonies than for surface colonies. The nature of the food matrix only exerted an influence on the maximum specific growth rate, which was significantly higher in the viscous systems than in the gelled systems. The presence of a small amount of fat droplets improved the growth of L. monocytogenes at 4 °C, resulting in a shorter lag phase and a higher maximum specific growth rate. The obtained results could be useful in the determination of a set of suitable microstructural parameters for future predictive models that incorporate the influence of food microstructure on microbial dynamics.

Journal of Food Microbiology © Elsevier after peer review. To access the final edited and published work see https://doi.Highlights 19 L. sakei CTC494 inhibited L. monocytogenes growth in sea bream fillets during 20 chilled and moderate abuse temperature storage. 21 L. sakei CTC494 did not increase deterioration of filleted sea bream at an initial 22 level of ≤ 4 log cfu/g. 23 L. sakei CTC494 showed potential as bioprotective culture for fish products. 24 An approach from broth to food was developed for modelling microbial 25 interaction. 26  Interaction models simulated L. monocytogenes inhibition by the bioprotective 27 L. sakei in filleted sea bream under static and dynamic temperature.28 29 30 31 32 33 34 35 36 37 Abstract 38 The objective of this work was to quantitatively evaluate the effect of Lactobacillus 39 sakei CTC494 (sakacin-producing bioprotective strain) against Listeria monocytogenes 40 in fish juice and to apply and validate three microbial interaction models (Jameson, 41 modified Jameson and Lotka Volterra models) through challenge tests with gilthead sea 42 bream (Sparus aurata) fillets under modified atmosphere packaging stored at isothermal 43 and non-isothermal conditions. L. sakei CTC494 inhibited L. monocytogenes growth 44 when simultaneously present in the matrix (fish juice and fish fillets) at different 45 inoculation ratios pathogen:bioprotector (i.e. 1:1, 1:2 and 1:3). The higher the 46 inoculation ratio, the stronger the inhibition of L. monocytogenes growth, with the ratio 47 1:3 yielding no growth of the pathogen. The maximum population density (N max ) was 48 the most affected parameter for L. monocytogenes at all inoculation ratios. According to 49 the microbiological and sensory analysis outcomes, an initial inoculation level of 4 log 50 cfu/g for L. sakei CTC494 would be a suitable bioprotective strategy without 51 compromising the sensory quality of the fish product. The performance of the tested 52 interaction models was evaluated using the Acceptable Simulation Zone approach. The 53 Lotka Volterra model showed slightly better fit than the Jameson-based models with 75-54 92 % out of the observed counts falling into the Acceptable Simulation Zone, indicating 55 a satisfactory model performance. The evaluated interaction models could be used as 56 predictive modelling tool to simulate the simultaneous behaviour of bacteriocin-57 producing Lactobacillus strains and L. monocytogenes; thus, supporting the design and 58 optimization of bioprotective culture-based strategies against L. monocytogenes in 59 minimally processed fish products.60 4

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The aim of this study was to model the growth and survival behaviour of Salmonella Reading and endogenous lactic acid bacteria on fresh pre-cut iceberg lettuce stored under modified atmosphere packaging for 10 days at different temperatures (4, 8 and 15 °C). The Baranyi and Weibull models were satisfactorily fitted to describe microbial growth and survival behaviour, respectively. Results indicated that lactic acid bacteria (LAB) could grow at all storage temperatures, while S. Reading grew only at 15 °C. Specific growth rate values (μmax) for LAB ranged between 0.080 and 0.168 h−1 corresponding to the temperatures 4 and 15 °C while for S. Reading at 15 °C, μmax = 0.056 h−1. This result was compared with published predictive microbiology models for other Salmonella serovars in leafy greens, revealing that predictions from specific models could be valid for such a temperature, provided they were developed specifically in lettuce regardless of the type of serovars inoculated. The parameter delta obtained from the Weibull model for the pathogen was found to be 16.03 and 18.81 for 4 and 8 °C, respectively, indicating that the pathogen underwent larger reduction levels at lower temperatures (2.8 log10 decrease at 4 °C). These data suggest that this Salmonella serovar is especially sensitive to low temperatures, under the assayed conditions, while showcasing that a correct refrigeration could be an effective measure to control microbial risk in commercial packaged lettuce. Finally, the microbiological data and models from this study will be useful to consider more specifically the behaviour of S. Reading during transport and storage of fresh-cut lettuce, elucidating the contribution of this serovar to the risk by Salmonella in leafy green products.